<template>
        <ul class="list">
            <li class="item" v-for="item in letters" :key="item"
            @click="handleLetterClick"
            @touchstart="handleTouchStart"
            @touchmove="handleTouchMove"
            @touchend="handleTouchEnd"
            :ref="item">{{item}}</li>
        </ul>
</template>

<script>
export default {
  name: 'Alphabet',
  props: {
    list: Object
  },
  computed: {
    letters () {
      const letters = []
      for (let i in this.list) {
        letters.push(i)
      }
      return letters
    }
  },
  data () {
    return {
      touchStatus: false,
      startY: 0,
      timer: null
    }
  },
  updated () {
    this.startY = this.$refs['A'][0].offsetTop
  },
  methods: {
    handleLetterClick (e) {
      this.$emit('change', e.target.innerText)
    },
    handleTouchStart () {
      this.touchStatus = true
    },
    handleTouchMove (e) {
      if (this.touchStatus) {
        if (this.time) {
          clearTimeout(this.timer)
        }
        this.timer = setTimeout(() => {
          const touchY = e.touches[0].clientY - 74
          const index = Math.floor((touchY - this.startY) / 20)
          if (index >= 0 && index < this.letters.length) this.$emit('change', this.letters[index])
        }, 16)
      }
    },
    handleTouchEnd () {
      this.touchStatus = false
    }
  }
}
</script>

<style lang="stylus" scoped>
@import '~styles/varibles.styl'
   .list
      display:flex
      flex-direction:column
      justify-content:center
      position :absolute
      top:1.56rem
      right:0
      bottom:0
      width:.4rem
      .item
          line-height :.4rem
          text-align :center
          color:$bgColor
</style>
